2 * Read-Copy Update mechanism for mutual exclusion
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, write to the Free Software
16 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
18 * Copyright IBM Corporation, 2001
20 * Authors: Dipankar Sarma <dipankar@in.ibm.com>
21 * Manfred Spraul <manfred@colorfullife.com>
23 * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
24 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
26 * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
27 * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
29 * For detailed explanation of Read-Copy Update mechanism see -
30 * http://lse.sourceforge.net/locking/rcupdate.html
33 #include <linux/types.h>
34 #include <linux/kernel.h>
35 #include <linux/init.h>
36 #include <linux/spinlock.h>
37 #include <linux/smp.h>
38 #include <linux/interrupt.h>
39 #include <linux/sched.h>
40 #include <asm/atomic.h>
41 #include <linux/bitops.h>
42 #include <linux/percpu.h>
43 #include <linux/notifier.h>
44 #include <linux/cpu.h>
45 #include <linux/mutex.h>
46 #include <linux/module.h>
47 #include <linux/kernel_stat.h>
55 static DEFINE_PER_CPU(struct rcu_head, rcu_barrier_head) = {NULL};
56 static atomic_t rcu_barrier_cpu_count;
57 static DEFINE_MUTEX(rcu_barrier_mutex);
58 static struct completion rcu_barrier_completion;
59 int rcu_scheduler_active __read_mostly;
61 static atomic_t rcu_migrate_type_count = ATOMIC_INIT(0);
62 static struct rcu_head rcu_migrate_head[3];
63 static DECLARE_WAIT_QUEUE_HEAD(rcu_migrate_wq);
66 * Awaken the corresponding synchronize_rcu() instance now that a
67 * grace period has elapsed.
69 void wakeme_after_rcu(struct rcu_head *head)
71 struct rcu_synchronize *rcu;
73 rcu = container_of(head, struct rcu_synchronize, head);
74 complete(&rcu->completion);
78 * synchronize_rcu - wait until a grace period has elapsed.
80 * Control will return to the caller some time after a full grace
81 * period has elapsed, in other words after all currently executing RCU
82 * read-side critical sections have completed. RCU read-side critical
83 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
86 void synchronize_rcu(void)
88 struct rcu_synchronize rcu;
90 if (rcu_blocking_is_gp())
93 init_completion(&rcu.completion);
94 /* Will wake me after RCU finished. */
95 call_rcu(&rcu.head, wakeme_after_rcu);
97 wait_for_completion(&rcu.completion);
99 EXPORT_SYMBOL_GPL(synchronize_rcu);
101 static void rcu_barrier_callback(struct rcu_head *notused)
103 if (atomic_dec_and_test(&rcu_barrier_cpu_count))
104 complete(&rcu_barrier_completion);
108 * Called with preemption disabled, and from cross-cpu IRQ context.
110 static void rcu_barrier_func(void *type)
112 int cpu = smp_processor_id();
113 struct rcu_head *head = &per_cpu(rcu_barrier_head, cpu);
115 atomic_inc(&rcu_barrier_cpu_count);
116 switch ((enum rcu_barrier)type) {
117 case RCU_BARRIER_STD:
118 call_rcu(head, rcu_barrier_callback);
121 call_rcu_bh(head, rcu_barrier_callback);
123 case RCU_BARRIER_SCHED:
124 call_rcu_sched(head, rcu_barrier_callback);
129 static inline void wait_migrated_callbacks(void)
131 wait_event(rcu_migrate_wq, !atomic_read(&rcu_migrate_type_count));
135 * Orchestrate the specified type of RCU barrier, waiting for all
136 * RCU callbacks of the specified type to complete.
138 static void _rcu_barrier(enum rcu_barrier type)
140 BUG_ON(in_interrupt());
141 /* Take cpucontrol mutex to protect against CPU hotplug */
142 mutex_lock(&rcu_barrier_mutex);
143 init_completion(&rcu_barrier_completion);
145 * Initialize rcu_barrier_cpu_count to 1, then invoke
146 * rcu_barrier_func() on each CPU, so that each CPU also has
147 * incremented rcu_barrier_cpu_count. Only then is it safe to
148 * decrement rcu_barrier_cpu_count -- otherwise the first CPU
149 * might complete its grace period before all of the other CPUs
150 * did their increment, causing this function to return too
153 atomic_set(&rcu_barrier_cpu_count, 1);
154 on_each_cpu(rcu_barrier_func, (void *)type, 1);
155 if (atomic_dec_and_test(&rcu_barrier_cpu_count))
156 complete(&rcu_barrier_completion);
157 wait_for_completion(&rcu_barrier_completion);
158 mutex_unlock(&rcu_barrier_mutex);
159 wait_migrated_callbacks();
163 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
165 void rcu_barrier(void)
167 _rcu_barrier(RCU_BARRIER_STD);
169 EXPORT_SYMBOL_GPL(rcu_barrier);
172 * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
174 void rcu_barrier_bh(void)
176 _rcu_barrier(RCU_BARRIER_BH);
178 EXPORT_SYMBOL_GPL(rcu_barrier_bh);
181 * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
183 void rcu_barrier_sched(void)
185 _rcu_barrier(RCU_BARRIER_SCHED);
187 EXPORT_SYMBOL_GPL(rcu_barrier_sched);
189 static void rcu_migrate_callback(struct rcu_head *notused)
191 if (atomic_dec_and_test(&rcu_migrate_type_count))
192 wake_up(&rcu_migrate_wq);
195 static int __cpuinit rcu_barrier_cpu_hotplug(struct notifier_block *self,
196 unsigned long action, void *hcpu)
198 if (action == CPU_DYING) {
200 * preempt_disable() in on_each_cpu() prevents stop_machine(),
201 * so when "on_each_cpu(rcu_barrier_func, (void *)type, 1);"
202 * returns, all online cpus have queued rcu_barrier_func(),
203 * and the dead cpu(if it exist) queues rcu_migrate_callback()s.
205 * These callbacks ensure _rcu_barrier() waits for all
206 * RCU callbacks of the specified type to complete.
208 atomic_set(&rcu_migrate_type_count, 3);
209 call_rcu_bh(rcu_migrate_head, rcu_migrate_callback);
210 call_rcu_sched(rcu_migrate_head + 1, rcu_migrate_callback);
211 call_rcu(rcu_migrate_head + 2, rcu_migrate_callback);
212 } else if (action == CPU_POST_DEAD) {
213 /* rcu_migrate_head is protected by cpu_add_remove_lock */
214 wait_migrated_callbacks();
220 void __init rcu_init(void)
223 hotcpu_notifier(rcu_barrier_cpu_hotplug, 0);
226 void rcu_scheduler_starting(void)
228 WARN_ON(num_online_cpus() != 1);
229 WARN_ON(nr_context_switches() > 0);
230 rcu_scheduler_active = 1;